The production of composite articles requires the use of pressure onto the blank for forming the blank over the forming tool. The forming member, such as a vacuum bag, is used to achieve said pressure such that wrinkles and trapped air in the blank can be forced out under vacuum pressure. The blank can be made by a so called “prepreg” material (layers or plies of fibre material previously impregnated with resin, such as thermosetting resin). The thermoforming apparatus comprising the forming member can be used for curing the resin of the blank in an autoclave or in an oven at elevated temperature and pressure. After curing the forming member is removed from the forming tool and the article can be removed.
It is desirable that the heat distribution in the blank is uniform during the forming process so that the forming cycle will be as short as possible. Today the use of an air circulation means is common in ovens or in autoclaves, but the lack of uniform heat distribution to the blank still exists.
One way of distributing heat in an apparatus is disclosed in WO 96/07532, wherein fluid is circulated in cavities under pressure for elevating the temperature of the composite lay-up.
However, there is a need for an improvement of apparatuses such as autoclaves, ovens or other thermoforming apparatuses using hot air for forming and curing the blank.
The object of the present invention is to overcome above-mentioned drawbacks and to develop known thermoforming apparatuses.